Did Global Warming Kill off the Dinosaurs?

Dinosaurs reigned supreme on Earth for hundreds of millions of years — many times longer than any human-like being has walked the face of our planet. But, roughly 66 million years ago, all non-avian dinosaurs (and about 75 percent of all life on dry land) was wiped out by a massive cataclysm. The question which perplexes paleontologists is — what happened?

The Chicxulub Crater off the Yucatán Peninsula of Mexico shows evidence that a giant asteroid, at least the size of Mount Everest, struck our planet right about the time the dinosaurs met their demise. A layer of iridium — an metal rare on Earth, but common in asteroids, is found at the K-T boundary, the layer of Earth deposited at the time non-avian dinosaurs went extinct. However, new research suggests massive volcanic eruptions in India, leading to massive global warming, may be the real culprit behind their disappearance.

“Everyone has heard that the dinosaurs died from an asteroid hitting the Earth. What many people don’t realize is that there have been many other mass extinctions in the last 500 million years, and many of them coincide with large volcanic outpourings,” said Blaire Schoene of Princeton University.

Tyrannosaurus Rex were among the last of the dinosaurs to walk the Earth, but even their mighty strength could not protect them from climate change. Image credit: AzDude/Pixabay

These eruptions emanate from large volcanoes known as flood basalts or large igneous provinces. Approximately 66 million years ago, the Deccan Traps, in what is now India, exploded in a massive volcanic eruption, burying the region in 3,350 meters (11,000 feet) of volcanic basalt rock, and pouring tremendous quantities of poisonous gas into the atmosphere. The amount of material released during these eruptions is hard to fathom — the events released enough lava to circle the Earth in a band one mile thick, and five miles wide. This is 675,000 times larger than the 2018 eruption of the Kilauea volcano in Hawaii.

The exact age of these deposits had never been carefully measured — until now. This finding provides strong evidence the eruptions may have played an important role in the disappearance of most dinosaurs from the face of the Earth. These ancient volcanic eruptions lasted roughly one million years — starting 400,000 years before the Chicxulub impact, and continuing until 600,000 years following the event. Researchers are pondering the role these eruptions may have played in changing the ecosystem prior to the impact with the asteroid.

Carbon dating — measuring the decay of carbon-14 in the remains of once-living beings, is not useful in dating 66-million-year-old rock. Instead, researchers studying geochronology (the ages of rocks) often depend on uranium-rich material in their samples. However, this method depends on finding rocks rich in the radioactive element, and basalt is usually poor in uranium. Dating volcanic flows often relies on silica-rich deposits, like those which pour from Mt. St. Helens.

The Deccan Traps in India, where massive volcanic eruptions may have doomed the dinosaurs. Image credit: Gerta Keller, Department of Geosciences, Princeton University

While in India, researchers studied fossilized soils caught between lava beds, and these contained the tiny zircon crystals that preserve radioactive uranium. This breakthrough led to a precise dating of the basalts, suggesting four distinct pulses of eruptions at the Deccan Traps may have played a critical role in the demise of dinosaurs. The release of sulfurous gases would have cooled the Earth in the short term, but carbon dioxide flooding the atmosphere would have led to a massive upswing in global temperatures. These climatic shifts, combined with the Chicxulub impact, may have been too much for non-avian dinosaurs to withstand, leading to their demise from the face of the globe.

So far, our planet has experienced five major extinctions, and we may be in the midst of a sixth such event.

The Ordovician period ended 444 million years ago, as the Earth was gripped by a short, severe ice age, likely caused by the uplift of the Appalachian Mountain range, This drop in temperatures led to a lowering of sea levels, wiping out 86 percent of the species on the planet.

Trilobites were one of the most successful and diverse of all early animals, but they were nearly wiped out 375 million years ago, as the oceans were starved of oxygen. Image credit: Adolofo-atm/Pixabay

Around 375–365 million years ago, Earth was experiencing the first flourishing of land plants around the globe. This likely led to the release of massive quantities of nutrients into the oceans, triggering algal blooms, sucking oxygen from the water, killing off 75 percent of the species on Earth.

The worst extinction in the history of the planet took place 251 million years ago, causing the demise of 96 percent of all species on the planet, and nearly ending life on Earth. A massive volcanic eruption in Siberia filled the atmosphere with carbon dioxide, causing temperatures to skyrocket, In response, methanogenic bacteria released tremendous quantities of methane into the atmosphere, further warming the globe. These events resulted in the acidification of the world’s oceans, which became stagnant, resulting in the release of hydrogen sulfide (the gas usually associated with the smell of rotten eggs). Biologists believe this event — which ended the Permian period — set back the evolution of life on Earth by 300 million years.

The least-understood of the five great extinctions ended the Triassic period sometime between 210 and 200 million years ago. No definitive cause has yet been found for this event that resulted in the loss of eight out of every 10 species then living on the face of the planet. However, this extinction led to the flourishing of dinosaur species around the globe.

The best-known extinction event, of course, is the one which ended the age of the dinosaurs. This ended the Cretaceous, and started the Tertiary, periods in the history of Earth. Paleontologists refer to this time as the K-T extinction (K stands for Cretaceous, as C denotes the Cambrian period).

Dinosaur species appear to have become less diverse in the 24 million years prior to the Chicxulub impact — evidence that volcanic eruptions in the Deccan Traps may have played a significant role in the disappearance of non-avian dinosaurs worldwide.

“[D]inosaurs showed a marked reduction in their ability to replace extinct species with new ones, making them vulnerable to extinction and unable to respond quickly to and recover from the final catastrophic event 66 [million years ago],” researchers reported in 2016.

NASA is searching for the origin of the asteroid which could have dealt the final blow to non-avian dinosaurs. One idea is the giant impactor may have been the result of a collision between two bodies in the asteroid belt. Image credit: NASA/JPL-Caltech

However, evidence that volcanoes may have played a significant role in the massive extinction which ended the age of the dinosaurs does not mean the asteroid impact was not the final chapter in their story. A person dying of cancer can still get hit by a bus. But, this new research may suggest volcanic eruptions — and global warming — may have played an important role in bring the age of the dinosaurs to a close.

On a brighter note, the loss of dinosaurs cleared the way for small, clever mammals to take dominion of the Earth, eventually leading to the rise of human beings.

Today, many biologists and climatologists have started to classify our current age as the sixth great extinction event in the history of the planet. The release of massive quantities of greenhouse gases into the atmosphere, combined with industrial and consumer waste, as well as agricultural runoff into the oceans, is leading to the greatest loss of species ever seen on Earth. Perhaps, millions of years from now, descendants of human beings may piece together the puzzle of what led to our great extinction.